Purge compositions are used in plastics processing equipment such as extrusion and injection molding equipment as a cleaning agent when the material which is being processed in the equipment is changed. For instance, in processing equipment, a change in the color of materials being processed requires removal of the material containing the first color before introduction of a material containing a second color. The purging compositions clean (remove) the first color from the system before introduction of the second color.
In some instances, the purging compositions should have sufficient viscosity to remove a material while not intermixing with that material. By not intermixing, the purging compositions can push the undesired materials out of the system.
U.S. Pat. No. 4,188,236 describes a process for producing non-dusting pigment compositions by contacting an aqueous dispersion of an organic pigment with a solution or dispersion of an alkaline-soluble rosin acid derivative, a sorbitan ester and a water-insoluble organic carder having a melting point below 100.degree. C. The pigment compositions can be used for coloring plastics, inks, paints, etc.
U.S. Pat. No. 5,157,067 describes liquid concentrates for incorporation into polymeric resins which comprise (1) a vehicle, preferably substantially free of water, comprising at least one organic rosin material and at least one surfactant, and (2) at least one colorant or additive. Optionally, the concentrates contain one or more organic diluents. The colorants may be organic or inorganic materials, and the additives include UV stabilizers or absorbers, antioxidants, fire retardants, blowing agents, antistats, lubricants, impact modifiers, mold release agents, filler/reinforcing materials (e.g., calcium carbonates) or mixtures thereof. A mixture comprising 70% of titanium dioxide, 13.5% of calcium carbonate, 10.5 % of a rosin material, 4.5 % of mineral oil, 0.9% of a suffactant and 0.6% of tinting pigments is described as an example of a liquid color concentrate which may be blended with a polymeric resin to color the resin.